The present invention relates to a biological transducer device having a thin film, high molecular piezoelectric element which provides excellent pliability for measuring blood pressure, pulse wave, pulse rate, intracardiac sound, and heart noise etc. The biological transducer is particularly suitable for contacting an artery of a living body for converting the vibration or sound of the living body into electrical signals.
The blood pressure is one of the many sources of information about a living body which can be obtained without entering a blood vessel. Heretofore, blood pressure is measured, in general, by the following method. A manschette or cuff is first wrapped around the arm of a human body and air is injected into the manschette by a hand operated air pump, to increase the pressure in the manschette until the sound or pulse in the artery beneath the manschette disappears. Then the pressure in the manschette is decreased slowly. The pressure in the manschette and the systolic blood pressure will be equal when a sound, called the Korotkov sound, synchronized with heart pulse, appears. The pressure in the manschette is also equal to diastolic blood pressure when this sound (i.e. Korotkov sound) disappears. However, in this prior method the Korotkov sound is detected by using a stethoscope in contact with the artery at a point near the manschette. The operator uses his judgement to determine by ear the pressure at the appearance or disappearance of the Korotkov sound so that great skill is needed for operation and detection of blood pressure and errors in judgement can easily occur.
Recently in the development of electronics, other detecting methods and means instead of the stethoscope method have been proposed and utilized. For example detecting devices employing direct transmitting means such as a strain gauge, a solid piezoelectric material (PZT, Rochelle salt etc.) or an air transmitting means such as micro-phone or optical means are proposed. However, these prior devices, including the stethoscope are only suitable for measuring at a particular spot and is necessary to skillfully and accurately contact the measuring point. Moreover, the mechanical impedance of the proposed transducer is larger than the mechanical impedance of the skin or cutis at the measuring point. Thus impedance matching is wrong so that these transducers hinder the movement in the artery, resulting in low detection sensitivity and poor reproduction (i.e. the same result can not be expected by repeating the measurement). Moreover, the transducer device employing a strain gauge or solid piezoelectric element is complicated in construction, sensitive to shock and can easily break.